We will continue our studies of the mechanism of prophage insertion of bacteriophage lambda into the DNA of Escherichia coli. In particular, we will determine (a) why DNA replication must be shut down, (b) why the Xis product must be eliminated, (c) the role of the Red gene when DNA replication is absent and (d) whether integrase makes two phosphoester cuts which are separated so that two complementary single strands are generated.